Messages in this thread | | | Date | Sun, 13 Jul 2008 04:18:36 -0400 (EDT) | From | George Glover <> | Subject | Re: Runtime accounting bug? |
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On Sun, 13 Jul 2008, Andrew Morton wrote:
> On Sun, 6 Jul 2008 14:00:22 -0400 (EDT) George Glover <hyperborean@comcast.net> wrote: > >> Hello, >> >> I run two copies (dual processor system) of "mprime" from the GIMPS >> project. After a while running (weeks?) the cumulative runtime reported by >> top increments faster than real time, then after a while (unknown how long) >> the value increments normally again. Then, maybe something overflows - but >> runtime accounting stops entirely even though the process is in the run state. >> >> (mprime is a cpu-bound low priority process like seti@home and friends.) >> >> I presently have a stuck process and a one that should soon start to >> increment faster than possible. >> >> I have verified that the "stuck" process is indeed running since it continues >> to generate output. >> >> Here is the "stuck" process: >> >> cat /proc/4126/stat; sleep 5; cat /proc/4126/stat >> 4126 (mprime) R 2984 4126 2984 34819 4126 4202496 16530 0 4 0 2124505930 661087 0 0 39 19 1 0 8442861 21483520 3733 4294967295 134512640 138881564 3220348480 3220345732 135248565 0 0 0 16386 0 0 0 17 1 0 0 0 0 0 > ^^^^^^^^^^ >> 4126 (mprime) R 2984 4126 2984 34819 4126 4202496 16530 0 4 0 2124505930 661087 0 0 39 19 1 0 8442861 21483520 3733 4294967295 134512640 138881564 3220348480 3220345736 135241038 0 0 0 16386 0 0 0 17 1 0 0 0 0 0 > ^^^^^^^^^^ > > yes? The 14th column, do_task_stat()'s cputime_to_clock_t(utime)?
Yup, that is what I discovered with a brief tour of the source I could find. That particular task started to count up again a few days later, however at an accelerated rate 1.4-1.6x real time measuring that 14th field. I am wondering if it is related to a timer problem that has been reported recently:
http://lkml.org/lkml/2008/7/9/330
I can't say I've noticed my system clock advancing any faster however, maybe it's affecting only of the cpus and my clock app runs on the other.
I've rebooted since I wrote the message, so it may be a while before repeat behavior.
> My suspicion wold be that some of the arithmetic in here: > > static cputime_t task_utime(struct task_struct *p) > { > clock_t utime = cputime_to_clock_t(p->utime), > total = utime + cputime_to_clock_t(p->stime); > u64 temp; > > /* > * Use CFS's precise accounting: > */ > temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime); > > if (total) { > temp *= utime; > do_div(temp, total); > } > utime = (clock_t)temp; > > p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime)); > return p->prev_utime; > } > > is suffering overflows at very high values of p->utime. > > It's a 32bit machine, yes?
Yes it is.
> It would useful to know what your values of TICK_NSEC, NSEC_PER_SEC and > USER_HZ are.
TICK_NSEC is 999848 NSEC_PER_SEC is 1000000000 USER_HZ is 100
Since the process did start ticking again I wonder if is not an overflow and related to that other post I linked. I don't know enough about the various areas to judge though.
Let me know what else I can do if anything,
George
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